Proton Conductivity Switch for Hydrogen-Bonding Octaaminotetraphenylene Salts Through Crystal–Amorphous Transformation During H₂O Sorption

The phosphate salt of octaaminotetraphenylene (OATP), [(H4OATP4+)(H2PO4–)4], was prepared. Single crystals were isolated with a crystal formula of (H4OATP4+)(H2PO4–)4(H3PO4)0.25·2.5H2O, whereas the powder sample at 300 K formed an amorphous salt of (H4OATP4+)(H2PO4–)4.0·nH2O with n = 1–2. In the anhydrous solids (n = 0), the formation of a hydrogen-bonding network of H2PO4– anions and the dielectric relaxation associated with the motional freedom of H2PO4– were observed. Adsorption–desorption isotherms of H2O at 298 K showed the transformation between anhydrous amorphous (H4OATP4+)(H2PO4–)4 and hydrous crystalline (H4OATP4+)(H2PO4–)4·6H2O, and the proton conductivity increased by 2 orders of magnitude after H2O adsorption. The proton conductivity of hydrous salt reached 7.58 × 10–5 S cm–1. The cation–anion salt in the amorphous–crystalline transformation exhibited proton conductivity switching phenomena with an ON/OFF ratio of about 100 upon H2O adsorption–desorption.